I'm sorry, I'm not sure what you mean. This unit is an aluminum tank, as indicated by the title and the first line of the Features: "5 Gallon No-Rust Aluminum Auxiliary Air Tank". It's also indicated by the part number- the last "A" in "AUX05A" means aluminum.

The steel version of the tank is AUX05- no "A", and the title and Features say: "5 Gallon Steel Auxiliary Air Tank".